Water Chemisty 201

Calcium Hardness
pH
Total Alkalinity
Sanitation
Chlorine Demand
Summary
Super Shocking
Lowering Alkalinity

Calcium Hardness: back

CH is basically the amount of Calcium in your water. The lower your CH, the higher your TA and pH need to be to have balanced water. The higher your CH, the lower your TA and pH need to be. The first thing you should do is test your CH in your tub. If you haven't filled your tub yet, test your tap water for CH using a drop test kit. If you have a water softener in your house, it will remove most of the Calcium in your water. That means you may get a different reading from your indoor sink then from the outdoor hose. Check both to make sure. If you have really bad well water i.e. lots of metals etc., you may want to fill your tub using the water softener water, then just add Calcium afterward. If your water is city treated water, you may be ok straight from the hose. Also, consider getting a pre-filter that attaches to your hose, and filters out some of the metals.

Water can be either Acidic, Balanced or Alkaline. If your water is not balanced, it could cause all kinds of problems. If it's too acidic it could cause corrosion. If it's too alkaline it could cause scaling. Both of which will reducing the effectiveness of your sanitizer. If your water is not balanced your water is not safe for you, or your tub. So it's really critical to get this correct.

There are four main parameters to keeping your water balanced. Water Temperature, Calcium Hardness (CH), Total Alkalinity (TA) and Potens Hydrogen (pH). Assuming your water temp is around 100 degrees, we'll just focus on CH, TA and pH. The best way to test these is with a Drop Test kit, like the one mentioned above. IMO Test Strips are just not accurate enough to test these, especially for a beginner.

Here's my recommendation. If your CH is much below 100 ppm, you should add calcium to bring it up to 130-150 range. If your CH is over 100, you can leave it alone and just make a note of what it is. The CH level will be used to determine your TA/pH levels. To raise Calcium you add Calcium Chloride, aka Calcium Increaser. You can find it at most Pool/Spa supply stores. The good news is you only need to add Calcium once per water change, because it will stay relatively the same until your next water change.

pH back

pH is the measure of acidity in your water. It's on a scale of 0 to 14, 7 being neutral. The human eye has a pH of 7.5, so the ideal range in Pools/Spas is 7.4-7.6 with a min of 7.2 and max of 7.8. However, and this is important, just because you have a pH of 7.5, doesn't mean your water is balanced. If your CH is too low, you could be corroding your hot tub heater. If your TA is too high, you could be forming scale in your tub. Both of which will reduce your sanitizer effectiveness. So it is very important to have balanced water along with an ideal pH.

Total Alkalinity: back

Alkalinity is a pH Buffer. High levels of TA will not allow pH to change from additions of acid or base. However, a high TA requires a low pH to have balanced water. On the other hand, very low levels of TA will allow the pH to change with very little acid. A very low TA level could cause your pH to drop to low levels, very fast with little acid. Also, the lower your TA, the higher your pH needs to be to have balanced water. So as you can see, a very low TA can become very unstable.

However, pH will have a tenancy to rise with aeration (i.e. use of jets and air), more so if your TA is high. Although, as long as you're not adding Acid (or anything with a lower pH) to your tub, the pH will not usually drop. Therefore, in hot tubs the problem is normally pH rise (or Drift), because of all the aeration. So the trick is to get the TA high enough to not create an unstable situation, and low enough to not allow pH to rise too much.

Let me repeat the last sentence, because it's the single most important thing to keeping your water balanced. The key to having balanced water, without pH drift, is having the correct TA level. If you find your pH rises too high (>8.0) after using your tub, your TA is too high, and needs to be lowered. If you find your pH is too low and/or your water is continually acidic, your TA is too low and needs to be raised. By fine tuning your TA, you can get your pH perfectly balanced, that rarely needs adjustment.

SO, what's a good TA then? That depends on your CH. If your CH is around 150 ppm, your TA would need to be 80 ppm for your water to be balanced with an ideal pH of 7.6. How did I come up with those numbers you ask? Easy, I went to The Pool Calculator website, and plugged in a Temp of 100, CH of 150, pH of 7.6 and adjusted TA until the CSI was close to zero. This website allows you to calculate your Saturation Index, based on the four Main parameters, Temp, CH, TA and pH. If CSI is less than zero you're acidic, if it's greater than zero you're alkaline and of it's close to zero your balanced.

OK, how do we adjust TA then? If TA is too low, you just add Baking Soda to raise it. However, if TA is high, it's little more involved. You'll need Acid (Dry or Muriatic). Depending on how high your TA is will depend on how long it will take you. Plan on it taking around an hour to decrease TA by 100 ppm. So if your TA is 300 ppm, plan it taking around 2-3 hours. First, uncover your tub and turn on all your jets, air, blowers, waterfalls etc. Test your pH. When it's greater than 7.8, add enough acid to bring it down to 7.0. Keep aerating until your pH is 7.8 again (about 30 min), then add more acid and repeat. Every time you add acid you're lowering your pH and TA. When you get your TA tuned perfectly, your pH will rise to a level (i.e. ~7.6) and stop, and then you know you're at your ideal TA level. If your pH is rising too high (>8.0), bring your TA down a little more. If your pH doesn't rise enough from aeration (after an hour or more), you over shot it and need to add a little Baking Soda to raise your TA. After a few days/weeks of monitoring it, you'll get your TA tuned perfectly. You may need to add a little Dry Acid once a week or two, but your water should be well balanced at that point.

I wouldn't go much below 50 ppm TA, because that could become unstable if you add any kind of acid. Also, if you have a very high TA, above 200, you may need to add more acid in the beginning to get your pH down. Remember, TA is a pH buffer, so the higher the TA, the more acid it takes to bring the pH down. It takes approximately 8 oz total of Dry Acid to bring TA down 100 ppm in a 350 Gal tub. However, the important thing is not to add too much acid all at once, causing your pH to drop below 7.0. That's why you should divide up the dosages, while aerating constantly. Also, if you lower your TA to 50-60, you will need to raise you CH to compensate.

Lastly, there is one more thing I haven't mentioned that you can add to your tub that will help buffer your pH, Borates. The easiest way to add Borates to your tub is to get a product called Gentle Spa. It is pH balanced, so there is no need to add acid to counter balance it. The ideal amount is ~50 ppm, and only needs to be added once per water change. That will help keep your pH from drifting from aeration. Not to mention, actually make your water feel silkier. I highly recommend it.

Sanitation back

I'm only going to discuss Chlorine here, because I don't know enough about Bromine to comment on it. This is based on Chem Geeks Dichlor/Bleach method. I have found this method to be very easy and safe to use. I have yet to have a problem. I don't want to get into pros and cons, because that's better suited for it's own thread. If you don't know his method, this should explain it to you. If you do know it, maybe this will help you execute it better. I'm not going to get too technical. I'm just going to discuss everything that's important to keep your tub sanitized easily. If you want more details, search through Chem Geek's posts. You'll have plenty to read. Disclaimer: I'm not trying to convince you to use this method. I'm just explaining it. Please weigh all options before making a decision.

There are really two main things happening when your pool/tub is being sanitized. Organic waste is being oxidized, and bacteria/viruses are being killed. Chlorine does both, very well. That's why it's the most popular sanitizer in pools and spas. However, in order for chlorine to be effective there needs to be a Free Chlorine (FC) level in your tub at all times. If it drops to zero, bacteria will multiple within hours. So the number one rule with using chlorine as a sanitizer is, never let it drop to Zero for any length of time. Now let's get started on the procedure.

The first thing we are going to use to sanitize our tub is Dichlor. Dichlor is actually two things, Chlorine and Cyanuric Acid (CYA). CYA is a chlorine stabilizer, which slows down dissipation from UV rays (sunlight). It also acts as a buffer to hold chlorine in reserve. Having CYA in your tub will stop the chlorine from dissipating as fast while waiting for something to do. However, CYA also cuts down on the ability for the chlorine to sanitize. So in other words, the higher the CYA level, the longer the FC will wait in the tub, but the less effective the FC is. With no CYA in the tub, using bleach would be too strong and not practical to use. So, there needs to be a happy medium. Luckily Chem Geek has come up with one for us. He suggests a CYA of ~20 ppm. Personally I use a CYA of 30 ppm for reasons I won't get into here. But I think Chem Geek would agree anywhere between 20-30 is fine. Where the problem comes in is when CYA gets too high (above 100) after weeks of using Dichlor. Then your FC needs to be really high to get the same sanitation effectiveness. That's why we switch to bleach after we get our CYA to 20-30. Bleach doesn't add anymore CYA.

So, I'm going to assume our target CYA is 30, but feel free to use 20 and adjust as necessary. I find that it's easier to keep track of how much Dichlor you're adding to the tub and calculate the CYA, rather than testing CYA with the drop test kit until you get a 30 ppm reading. For every 10 ppm of Dichlor you add to your tub, you add 9 ppm CYA. So roughly 34 ppm Dichlor will give you 30 CYA. On a fresh fill, and after your water is balanced by the above method, shock your tub with Dichlor to 10 ppm FC. Then over the course of the next days, depending on bather load, add 24 ppm more FC using Dichlor. You want to keep your FC normally between 3-6 ppm everyday. This means you will be testing your FC EVERYDAY.

For example: On one day you test your FC and its 1 ppm. You'll then add 5 ppm FC to bring it to 6. The next day you test FC and its 3. You then add 3 ppm FC. You will do this until you add a total of 34 ppm FC to your tub using Dichlor. After that, you then switch to using bleach (Clorox Regular Unscented). Important: if you're not willing to test your tub every day, at least for the first month or two, this method is not for you. I'd recommend another sanitation method

When you use your tub (this applies to when you are still using Dichlor or after you switch to bleach), the rule of thumb is, and you'll use approximately 7 ppm FC per person per hour in a 350 gal tub. Now this will depend on a lot of things, water temp, cleanliness of the users etc. If it's just two people, after taking showers, using no swimsuits, with the temp at 98 you may only need 2 ppm FC/person/hour. However, if you have 6 people in their clothes, drinking (spilling) beer, with a temp at 102 causing everyone to sweat, you may need 20 ppm FC/person/hour. So this is where you may need to make a judgment call and/or experiment. Remember, the Chlorine has to do two things, Oxidize Waste, and Kill Bacteria. If your tub is being subjected to a lot of waste (sweat, beer etc), your FC will be used up and not be able to kill bacteria. Not good! So I'll give you two scenarios and how you might go about running an experiment. Remember, all this up front work is only necessary in the beginning, until you learn how much FC is being used in your tub. Once you know, it becomes easy to maintain. The rule of thumb is, assuming CYA is 20-30 ppm, FC should normally be between 3-6, with a min of 1 and shock to 12 once a week.

We'll go with the easy one first, two people, showered, no suits etc. (Note: Some people prefer to use the tub with very little FC. That's your choice. I'm just telling you how to determine how much FC you're using in a safe manner). Test your FC and add Chlorine to get to 5 ppm FC. After one hour of soaking test FC again. If you find you have no FC after an hour, next time start with 6 or 7. If you find you still have 3 ppm FC, next time it's safe to start with 3-4 ppm FC. Get it? The trick is to have the lowest amount of FC without ever dropping to zero. If you plan on staying in the tub longer than an hour, either start out with more FC, or add some during the soak. However, you don't want to get into the tub with the FC much above 8, unless of course you like a strong smell of chlorine. I got in once with FC at 10, and it was a little too much for me, and I like the smell of Chlorine.

On the other extreme. Full tub of people drinking, sweating etc. Do the same as above, but start out with more FC, maybe 6-8 ppm. Check the FC in an hour (or even a half). If you have no FC, you need to add some and check more often. If you still have FC, add some, and check again in the same time frame. It's the same as above, but you're just using more FC, more often. However, having the FC drop to zero for a short time with your lover, is not the same as with 4-5 other people, if you get my drift. So it's much more important to keep FC above zero at all times during a Hot Tub Party.

If you find you're having trouble keeping FC in your tub during parties, and/or you smell a foul odor during your soaks, you can add Potassium Monopersulfate (MPS or Non-Chlorine Shock) before (and/or during) your soak to help the Chlorine Oxidize waste. The only thing I would say is, go easy with MPS. Use only the amount needed and not much more. It is acidic and will lower your TA/pH if you use a lot. Start out with 1-2 tbs in addition to your normal FC, and see if that cuts down on the FC usage. Up it to 3-4 tbs, or add another 1-2 tbs during the soak if needed. MPS will help oxidize waste. However, it will not kill bacteria, so you still need FC. Also, you can use MPS as a shock once a week to help oxidize leftover waste, and reduce Combined Chlorine (spent FC).

After a month or two you will learn a routine, and be able to add Chlorine less often (i.e. every 2-3 days). How often you need to add Chlorine will depend on your Chlorine Demand (CD). The lower the CD, the less often you need to add Chlorine. The key is to keep CD as low as possible. HERE is a link that describes Chlorine Demand in detail, how to measure it and how to keep it low.

Wow if you made it this far, you did pretty well. It seems like a lot to learn, but it's really not. I'll summarize it here.

SUMMARY back

Water Balance

If your CH is much below 100 ppm, raise it to ~150 ppm. Otherwise, make a note of it.
Adjust your TA to ~80 ppm to start with then fine tune from there. Use Baking Soda to raise it, or Acid/Aeration method to lower it. It takes ~8 oz Dry Acid to lower TA by 100 ppm in a 350 Gal Tub. Don't add all at once! If you lower your TA, you may need to raise your CH to compensate.
pH should be between 7.2-7.8. Aerate to Raise pH. Acid to lower it.
If pH creeps up too much (>8.0), lower TA. If pH is too low, and doesn't raise enough by aeration, raise TA.
Add ~50 ppm Borate. (Borox/Acid or Gentle Spa)
Calcium, Baking Soda, Dry Acid and Borates is all you need to balance your water.


Sanitation

On a fresh fill use Dichlor until you get to 20-30 ppm CYA. (10 ppm FC = 9 ppm CYA)
Then switch to Clorox Unscented 6% bleach.
Never let FC drop to Zero for any length of time. Keep it between 3-6 ppm normally, min of 1 ppm, and shock to 12 ppm once a week.
Use MPS if needed before hot tub parties and/or once a week to help oxidation. Don't use more than needed, because it's acidic and may lower your TA/pH.
Check your Chlorine Demand, and keep it low.
Dichlor, Bleach and MPS are all you need to keep your tub sanitized.


Lastly, get a drop test kit such as the Taylor K-2006. Also get FC test strips. They come in handy for a quick FC estimate, during party's etc. The only two things you need to check regularly are FC and pH. Check them every day and after soaks. Adjust TA as needed. If you have your water well balanced, you'll rarely need to adjust your TA. You'll just be adding chlorine every day, and after soaks. Shock once a week, and/or after high bather loads. Use MPS if you have parties, and/or don't want to use as much chlorine. Keep Chlorine Demand low, and you can add Chlorine every 2-3 days. Easy as can be, and your tub is always ready.

I hope that helps you to understand Water Maintenance a little better. It helped me just to write. If I missed anything important please let me know, I'll be happy to add it.

LOWERING TOTAL ALKALINITY back

This topic comes up quite a bit. I explain the process in our Maintenance Guide, but we thought we'd post a separate thread for easy reference. We won't get into detail why you would want to do this here. See our guide for more info. We will say this, the key is, you should NOT focus on adjusting pH directly. Instead, you should focus on adjusting TA to an ideal level, in order to keep your pH in line.

The problem with lowering Total Alkalinity (TA) is that when you add acid to lower TA, pH also decreases. This limits the amount you can lower TA without pH becoming too low. However, there is something you can do to raise pH that leaves TA alone, Aeration. Aeration is the process of turning on all the jets and air features in your tub, in order to pump as much air into the water as possible. By adding Acid and Aerating you can lower TA, while keeping pH the same.

One thing to remember is, the amount that TA decreases is directly proportional to the amount of acid you add. That is, in a 350 gal tub, 8 oz of Dry Acid will lower TA by 100ppm. It is important to know (by calculating) how much Total Acid you need to add to your tub in order to get to your Target TA.

The other thing to remember is, the higher your TA, the less effect acid will have on your pH. If your TA is high, adding acid won't affect it much. This confuses some beginners (and experts alike), which causes them to give up on lowering their pH. Because of this, you need to add more Acid in the beginning, and less as you get closer to your Target TA.

So, let's get started. Here is the process.

1. Turn on all your jets and air features and keep them on the entire process. (i.e. Aerate)
2. Calculate how much you want to lower your TA, and how much acid you need to add to lower it.
3. Add to the tub HALF (not > 1 cup nor < 1 TBS) of the amount of the remaining acid you need to add.
4. Aerate for 30min, and check TA/pH.
5. If TA > Target and pH is > 7.8, go to step 2.
6. If TA > Target and pH is < 7.6, go to step 4 one time.
7. If TA > Target and you can't get pH > 7.8 via aeration, Target too low. Stop here.
8. If TA = Target and pH is > 7.8, Target too high. Lower Target TA and go to step 2.

Example:
Your TA is 300ppm, you want to lower it to 60ppm, in a 350 gal tub.
To lower TA by 240 ppm you need to add a total of 2.4 cups (~19oz) dry acid.

Turn jets/air on.
Add 1 cup acid and Aerate 30mins.
Check TA/pH. TA=200 and pH>8.0
Add 6 oz acid and Aerate 30mins.
Check TA/pH. TA=125 and pH>8.0
Add 3 oz acid and Aerate 30mins.
Check TA/pH. TA=90 and pH>8.0
Add 2 oz acid and Aerate 30mins
Check TA/pH. TA=65 and pH=7.8
Add 1 TBS acid and Aerate 30mins
Check TA/pH. TA=60 and pH=7.6

The main thing to remember is, you add more acid in the beginning of the process, and taper off toward the end. This method will allow you to lower your TA in a matter of a few hours regardless of how high your TA is.

Lastly, safety is priority one. Be careful with any type of acid, especially Muriatic. If you're using Muriatic acid, wear rubber gloves and eye protection. Muriatic Acid is nasty stuff. Dilute all acid in a bucket of water and slowly pour mixture over a return flow, or middle of tub. Be careful not to splash. When mixing Acid and Water, always add Acid to water! NEVER ADD WATER TO ACID!!!

Chlorine Demand is the single most important measurement you can make, to determine the health of your tub water. back

Any organic "stuff" (dead or alive) in your tub, Chlorine will kill and oxidize. The more "stuff" in your tub, the more Chlorine is needed. The question becomes, is there a measurement of how much "stuff" there is in your tub. Yes, Chlorine Demand (CD)! CD is basically how much Chlorine (sanitizer) your tub is using. This also applies to Bromine. CD will tell you how much Chlorine is being used, and therefore tell you how much "stuff" is in your tub.

Now that we know what CD is, how do we measure it? That's the easy part.

1st, Shock your tub to around 10ppm FC, and make note of where it's at.
2nd, Cover and let sit for 24hrs. DON'T use the tub!
3rd, the next day, test FC again.

Now, take the 2nd measurement and divide it by the 1st measurement. This will give you a percentage of how much Chlorine is left in your tub after one day. Obviously the higher percentage the better. 100% means your tub is not using ANY Chlorine (not likely). 0% means your tub used ALL the Chlorine you put in it (NOT GOOD).

To take it one step further you can calculate CD, which is one minus the Percentage you calculated. That will give you the percentage of Chlorine your tub is using. Obviously the LOWER the better. If it's 0%, that means your tub is using 0% of the Chlorine (again not likely). If it's 100%, that means your tub used 100% of the Chlorine you put in (again NOT GOOD).

Measuring CD is the easy part. Interpreting it is a little trickier. It's best to first measure CD on a fresh refill, BEFORE you use the tub. That way you have a good Baseline (BL). My BL is ~25%. That means, when I shock my tub to 10ppm FC, the next day it is ~7.5ppm. After you start using your tub, the CD will increase. The trick is to try to keep it as close to your BL as possible.

For example, let's say you use the tub (4 people for an hour). After you get out, you shock the tub to 10ppm. The next day you check FC and its 2ppm. That means your CD is 80%. That's too high and means you didn't use enough Chlorine the night before. Not a problem, just shock to 10ppm again. The next day check your FC. It should be above 5ppm. If not, keep shocking until it is. If you're not using enough Chlorine, your CD will increase and be more difficult to get back down.

So what's a good CD then? Here's my recommendation.
~25% is Ideal. This should be your Baseline.
~50% is Ok. This is probably where most people are at.
~75% is Poor. This means "something" is using up chlorine too fast. You need to shock.
100% is bad. This could mean you just had a Hot Tub Party, you've been using way too little Chlorine, OR you have "something" actively growing (a bug) in your tub. The former two mean you should start shocking. The latter means you need to decontaminate your tub.

NEVER let your CD get to 100%, or you'll have problems. Also, the older your water gets, the more difficult it will be to lower the CD. If you find it difficult to lower your CD, it could mean you're due for a water change. It could also mean your filter is dirty and needs to be cleaned. Make sure your keep you filter clean, or it will use up Chlorine. Lastly, MPS will help Chlorine oxidize waste, and therefore lower your CD. So if you're using MPS, you may want to wait a few days (week) before you measure CD. If you find it difficult to lower CD, try shocking with MPS.

Hope that helps you keep you water cleaner.

SUPER SHOCKING back

This topic comes up quite a bit, so we thought we'd post a How To guide.

Decontamination is the process of Super Shocking to Kill and Oxidize everything in your tub. There are two reasons why you would want to do this. One is your tub contains an excess amount of organic waste, and is using large amounts of sanitizer. The other is you have bacteria actively growing in your tub that has formed a protective shield (Biofilm), and cannot be killed from normal sanitation levels. The former is easy to tell by measuring sanitation levels, but the latter is more difficult (usually not until after you start getting sick).

This may sound extreme to some, but I recommend decontaminating any used tub that changes hands. You have no way of knowing how a used tub was maintained before you got it. Why chance getting sick?!? You have nothing to lose, and nice clean, safe tub to gain.

So how do you do decontamination?!? Here's how.

1. Use an enzyme to clean out your pipes, such as Swirl Away, Spa Flush etc. Add this product, run the jets 30 minutes and let sit overnight. It will clean out your pipes and deposit the gunk along the water line. Wipe the waterline with a dry paper towel or cloth. Make sure you remove your filter before adding this product. Better yet, buy a new filter.
2. The next day, drain your tub and clean the walls with some leftover enzyme from step one.
3. Refill tub as high as possible (above the normal waterline) with fresh water.
4. Balance your water at this point. TA = 80 ppm and pH = 7.2. If your pH is too far out of range, it will decrease the effectiveness of the Chlorine.
5. Add 50 ppm FC using Regular Clorox 6% Unscented Bleach. That's approx. 1/4 gal (32 oz) per 350 gal tub.
6. Run all jets and air features for 30-60 minutes. You can turn the air on and off every 10 minutes, to help clean the air lines.
7. Cut the power and drain the tub. This water is highly chlorinated, so you may want to keep it away from vegetation.
8. While the tub is draining clean the cover and all shell surfaces with the super chlorinated water. Then rinse well.
9. Refill tub with fresh water.
10. Balance water.

Test your Chlorine Demand to make sure the Decontamination worked by doing the following.
11. Shock with Dichlor (Stabilized Chlorine) to 10 ppm FC. Don't use the tub, let the jets run 10 minutes, cover and let sit 24 hours.
12. Check FC. If FC is 5 ppm or above, you're ok. If it's zero, your tub is still using excess Chlorine, and needs to be decontaminated again (Absent the Spa Flush). However, this should be rare.

After this procedure your tub should be clean like new. If you maintain your water properly, your should never have to do this again.